1. Field of the Invention
This invention relates generally to magnetic resonance force microscope, and more particularly, to a magnetic resonance force microscope that is particularly adapted to study biological systems, such as isolated cells, sub-cellular organelles and other sub-cellular structures, or cellular receptors and proteins, at resolutions ranging from 1 micron to 1 xc3x85.
2. Description of the Related Art
Magnetic resonance force microscopy (MRFM) is an emerging technology that combines the strengths of magnetic resonance and force microscopy to achieve high resolution three-dimensional sub-surface imaging of a test substance.
Magnetic resonance imaging (MRI) has had a revolutionary impact on non-invasive imaging for both medical purposes and for microscopic studies of biological systems. However, the relative insensitivity of inductive detection via rf coils prevents conventional MRI techniques from achieving resolution better than 10 microns. Recent theoretical and experimental work has shown that any magnetic resonance experiment, originally performed using conventional inductive techniques, can also be performed using microscale mechanical resonators and the technology of force microscopy. While current inductive detection limits are on the order of about 1015 nuclear spins, mechanical detection is revolutionary because the theoretical sensitivity is a single nucleon.
To date, both electron and nuclear magnetic resonance signals have been successfully detected by mechanical means, validating the theory of mechanical detection of magnetic resonance. In these early experiments, a microscale force microscope cantilever detects the magnetic force exerted by electron or nuclear moments in the material being observed. The magnetization of the material was modulated by the resonant frequency of the cantilever by standard magnetic resonance techniques.
Currently, several laboratories are developing the technology for application to the study of semiconductor chips and related areas in materials science applications. While researchers have expressed the desirability of imaging biological systems with this technology, there has been no practical reduction to practice of a magnetic resonance force microscope adapted to analyze biological materials.
Nevertheless, the impact of magnetic resonance force microscopy technology on biomedical research and biotechnology would be substantial. For example, an MRFM would be a powerful new probe for use in the fields of pathology and histology. Typically, tissue biopsy samples are prepared for diagnostic evaluation by thinly slicing the sample, followed by numerous staining procedures, and finally by carefully mounting of the samples for optical microscopy. The three-dimensional imaging capability of an MRFM would facilitate the diagnostic process by eliminating the need to thinly slice biopsy samples. In addition, it is anticipated that the chemical specificity of the MRFM technology would allow the evaluation and development of new information on tissue biochemistry without the use of stains. The same capabilities would be extremely useful in the study of cellular and sub-cellular structure and function. Much of the analytical work in this field is also performed with optical microscopy techniques which are limited in their usefulness when studying thick or opaque samples and which are generally not chemical specific.
At the present time the primary tools employed for large biomolecular structure determination are x-ray and neutron crystallography. These probes require large quantities of material in the form of a crystal. Isolating and crystallizing sufficient quantities for obtaining biomolecular structures can be exceptionally time consuming. Months, or even years, may be required to determine such structures. The ability to directly image single-copy molecules by MRFM would dramatically reduce this time and would greatly accelerate the current pace of research.
It is, therefore, an object of this invention to provide a magnetic resonance force microscope specifically adapted to the study of biological systems.
It is another object of this invention to provide a technique for using magnetic resonance force microscopy to perform high resolution, chemical specific imaging of biological systems.
It is also an object of this invention to provide magnetic resonance force microscope and technique for using the same to image biological systems with resolutions of from about I micron to several nanometers, and potentially to molecular scale resolution.
The foregoing and other objects are achieved by this invention which provides in a broad apparatus aspect thereof, an MRFM apparatus for high resolution imaging of samples comprising:
a mechanical oscillator having a natural frequency of oscillation;
a sample containing nuclear or electron spins, in proximity to the mechanical oscillator;
means for applying a large substantially time independent magnetic field gradient to said sample;
means for applying at least one oscillating time dependent magnetic field to said sample;
means for detecting the low amplitude mechanical resonance signals from the sample.
In a preferred embodiment, the MRFM apparatus is adapted to image biological specimens as will be described more completely hereinbelow.
In a particularly preferred method of use, a biological sample is imaged by mechanical detection of magnetic resonance, by the steps of:
placing a sample containing nuclear or electron spins, in proximity to a mechanical oscillator having a natural frequency of oscillation;
applying a large substantially time independent magnetic field gradient to said sample;
applying at least one oscillating time dependent magnetic field to said sample; and
detecting the low amplitude mechanical resonance signals from the sample.
Scanning, by moving the sample and/or oscillator relative to one another, produces multi-dimensional images of the biological sample.
In certain embodiments of the invention, the biological specimen is altered to enhance its ability to be detected by the MRFM apparatus of the present invention. In the case of electron spin resonance, the biological specimen is doped with a paramagnetic agent. In the case of NMR imaging, the biological specimen is doped with a NMR visible compound.